Pyrrolic clefts

In an attempt to more fully understand the interactions between these novel pyrrolic clefts with anions, in particularly the observed high oxo-anion affinity, 2-amido-5-methylpyrrole analogues 3 and 4 were synthesized Figure 4)4... 

Denuault, G., Gale, P. A., Hursthouse, M. B., Light, M. E., Warriner, C. N. (2002) Anion complexation and elctrochemical behaviour of ferrocene-appended amido-pyrrole clefts, New. J. Chem. 26, 811-813. 

Silver(I) complexes with macrocyclic nitrogen ligands are also very numerous. Mono- or homodi-nuclear silver-containing molecular clefts can be synthesized from the cyclocondensation of functionalized alkanediamines or triamines with 2,6-diacetylpyridine, pyridine-2,6-dicarbalde-hyde, thiophene-2,5-dicarbaldehyde, furan-2,5-dicarbaldehyde, or pyrrole-2,5-dicarbaldehyde in the presence of silver(I).486 97 The clefts are derived from bibracchial tetraimine Schiff base macrocycles and have been used, via transmetallation reactions, to complex other metal centers. The incorporation of a range of functionalized triamines has provided the conformational flexibility to vary the homodinuclear intermetallic separation from ca. 3 A to an excess of 6 A, and also to incorporate anions as intermetallic spacers. Some examples of the silver(I) complexes obtained are shown in Figure 5. 

In contrast, Ni[pz(iV-Me2)8] C60 (lOOd) has a totally different supramolecular structure featuring a noncentrosymmetric 1 1 complex with a strongly warped pz unit. The plane of diametrically opposite pyrrole rings is being rotated by -30° with respect to each other about their N—N vectors with the nickel and the four coordinated nitrogen atoms are coplanar to within 0.006 A. Each C60 unit lies within a cleft formed by two steeply inclined (by -12°) Ni-pz molecules (Fig. 33), the shortest Ni—C (C60) distances are 3.29 and 3.64 A. 

Figure 3. First generation 2,5-diamido-lH-pyrrolic amide clefts.

A more recent development has been the synthesis of bisamidopyrrolylmethane based anion receptor systems (Figure 19).15 These receptors might be regarded as containing half a calix[4]pyrrole combined with die 2-amido appendages in common with the pyrrolic amide cleft. Compounds 19 and 20 were synthesized by reaction of diethyl-5,5 -methylenebis(4-ethyl-3-methyl-2-pyrrole) carboxylate with aniline or n-butylamine in the presence of trimethylaluminium in dry dichloromethane at 35°C in 40 and 43% respective yields. 

Pyrrole-containing receptors include porphyrins, extended porphyrins and calix[n]pyrroles. A variety of calixpyrroles have been used as sensors and in anion-separation technologies. An interesting example is the cryptand-like calixpyrrole (2.69) that binds fluoride via six of the nine hydrogen atoms, forming a one-to-one host-guest complex in dichloromethane and THF mixed solvent. The actual stoichometry is rather complicated as each of the pairs of clefts can bind fluoride ions, forming one-to-one, one-to-two or one-to-three stoichiometries. 

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